--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lld/ELF/InputFiles.cpp	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,1634 @@
+//===- InputFiles.cpp -----------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "InputFiles.h"
+#include "Driver.h"
+#include "InputSection.h"
+#include "LinkerScript.h"
+#include "SymbolTable.h"
+#include "Symbols.h"
+#include "SyntheticSections.h"
+#include "lld/Common/DWARF.h"
+#include "lld/Common/ErrorHandler.h"
+#include "lld/Common/Memory.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/CodeGen/Analysis.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Module.h"
+#include "llvm/LTO/LTO.h"
+#include "llvm/MC/StringTableBuilder.h"
+#include "llvm/Object/ELFObjectFile.h"
+#include "llvm/Support/ARMAttributeParser.h"
+#include "llvm/Support/ARMBuildAttributes.h"
+#include "llvm/Support/Endian.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/TarWriter.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+using namespace llvm::ELF;
+using namespace llvm::object;
+using namespace llvm::sys;
+using namespace llvm::sys::fs;
+using namespace llvm::support::endian;
+
+namespace lld {
+// Returns "<internal>", "foo.a(bar.o)" or "baz.o".
+std::string toString(const elf::InputFile *f) {
+  if (!f)
+    return "<internal>";
+
+  if (f->toStringCache.empty()) {
+    if (f->archiveName.empty())
+      f->toStringCache = std::string(f->getName());
+    else
+      f->toStringCache = (f->archiveName + "(" + f->getName() + ")").str();
+  }
+  return f->toStringCache;
+}
+
+namespace elf {
+bool InputFile::isInGroup;
+uint32_t InputFile::nextGroupId;
+std::vector<BinaryFile *> binaryFiles;
+std::vector<BitcodeFile *> bitcodeFiles;
+std::vector<LazyObjFile *> lazyObjFiles;
+std::vector<InputFile *> objectFiles;
+std::vector<SharedFile *> sharedFiles;
+
+std::unique_ptr<TarWriter> tar;
+
+static ELFKind getELFKind(MemoryBufferRef mb, StringRef archiveName) {
+  unsigned char size;
+  unsigned char endian;
+  std::tie(size, endian) = getElfArchType(mb.getBuffer());
+
+  auto report = [&](StringRef msg) {
+    StringRef filename = mb.getBufferIdentifier();
+    if (archiveName.empty())
+      fatal(filename + ": " + msg);
+    else
+      fatal(archiveName + "(" + filename + "): " + msg);
+  };
+
+  if (!mb.getBuffer().startswith(ElfMagic))
+    report("not an ELF file");
+  if (endian != ELFDATA2LSB && endian != ELFDATA2MSB)
+    report("corrupted ELF file: invalid data encoding");
+  if (size != ELFCLASS32 && size != ELFCLASS64)
+    report("corrupted ELF file: invalid file class");
+
+  size_t bufSize = mb.getBuffer().size();
+  if ((size == ELFCLASS32 && bufSize < sizeof(Elf32_Ehdr)) ||
+      (size == ELFCLASS64 && bufSize < sizeof(Elf64_Ehdr)))
+    report("corrupted ELF file: file is too short");
+
+  if (size == ELFCLASS32)
+    return (endian == ELFDATA2LSB) ? ELF32LEKind : ELF32BEKind;
+  return (endian == ELFDATA2LSB) ? ELF64LEKind : ELF64BEKind;
+}
+
+InputFile::InputFile(Kind k, MemoryBufferRef m)
+    : mb(m), groupId(nextGroupId), fileKind(k) {
+  // All files within the same --{start,end}-group get the same group ID.
+  // Otherwise, a new file will get a new group ID.
+  if (!isInGroup)
+    ++nextGroupId;
+}
+
+Optional<MemoryBufferRef> readFile(StringRef path) {
+  // The --chroot option changes our virtual root directory.
+  // This is useful when you are dealing with files created by --reproduce.
+  if (!config->chroot.empty() && path.startswith("/"))
+    path = saver.save(config->chroot + path);
+
+  log(path);
+
+  auto mbOrErr = MemoryBuffer::getFile(path, -1, false);
+  if (auto ec = mbOrErr.getError()) {
+    error("cannot open " + path + ": " + ec.message());
+    return None;
+  }
+
+  std::unique_ptr<MemoryBuffer> &mb = *mbOrErr;
+  MemoryBufferRef mbref = mb->getMemBufferRef();
+  make<std::unique_ptr<MemoryBuffer>>(std::move(mb)); // take MB ownership
+
+  if (tar)
+    tar->append(relativeToRoot(path), mbref.getBuffer());
+  return mbref;
+}
+
+// All input object files must be for the same architecture
+// (e.g. it does not make sense to link x86 object files with
+// MIPS object files.) This function checks for that error.
+static bool isCompatible(InputFile *file) {
+  if (!file->isElf() && !isa<BitcodeFile>(file))
+    return true;
+
+  if (file->ekind == config->ekind && file->emachine == config->emachine) {
+    if (config->emachine != EM_MIPS)
+      return true;
+    if (isMipsN32Abi(file) == config->mipsN32Abi)
+      return true;
+  }
+
+  if (!config->emulation.empty()) {
+    error(toString(file) + " is incompatible with " + config->emulation);
+    return false;
+  }
+
+  InputFile *existing;
+  if (!objectFiles.empty())
+    existing = objectFiles[0];
+  else if (!sharedFiles.empty())
+    existing = sharedFiles[0];
+  else
+    existing = bitcodeFiles[0];
+
+  error(toString(file) + " is incompatible with " + toString(existing));
+  return false;
+}
+
+template <class ELFT> static void doParseFile(InputFile *file) {
+  if (!isCompatible(file))
+    return;
+
+  // Binary file
+  if (auto *f = dyn_cast<BinaryFile>(file)) {
+    binaryFiles.push_back(f);
+    f->parse();
+    return;
+  }
+
+  // .a file
+  if (auto *f = dyn_cast<ArchiveFile>(file)) {
+    f->parse();
+    return;
+  }
+
+  // Lazy object file
+  if (auto *f = dyn_cast<LazyObjFile>(file)) {
+    lazyObjFiles.push_back(f);
+    f->parse<ELFT>();
+    return;
+  }
+
+  if (config->trace)
+    message(toString(file));
+
+  // .so file
+  if (auto *f = dyn_cast<SharedFile>(file)) {
+    f->parse<ELFT>();
+    return;
+  }
+
+  // LLVM bitcode file
+  if (auto *f = dyn_cast<BitcodeFile>(file)) {
+    bitcodeFiles.push_back(f);
+    f->parse<ELFT>();
+    return;
+  }
+
+  // Regular object file
+  objectFiles.push_back(file);
+  cast<ObjFile<ELFT>>(file)->parse();
+}
+
+// Add symbols in File to the symbol table.
+void parseFile(InputFile *file) {
+  switch (config->ekind) {
+  case ELF32LEKind:
+    doParseFile<ELF32LE>(file);
+    return;
+  case ELF32BEKind:
+    doParseFile<ELF32BE>(file);
+    return;
+  case ELF64LEKind:
+    doParseFile<ELF64LE>(file);
+    return;
+  case ELF64BEKind:
+    doParseFile<ELF64BE>(file);
+    return;
+  default:
+    llvm_unreachable("unknown ELFT");
+  }
+}
+
+// Concatenates arguments to construct a string representing an error location.
+static std::string createFileLineMsg(StringRef path, unsigned line) {
+  std::string filename = std::string(path::filename(path));
+  std::string lineno = ":" + std::to_string(line);
+  if (filename == path)
+    return filename + lineno;
+  return filename + lineno + " (" + path.str() + lineno + ")";
+}
+
+template <class ELFT>
+static std::string getSrcMsgAux(ObjFile<ELFT> &file, const Symbol &sym,
+                                InputSectionBase &sec, uint64_t offset) {
+  // In DWARF, functions and variables are stored to different places.
+  // First, lookup a function for a given offset.
+  if (Optional<DILineInfo> info = file.getDILineInfo(&sec, offset))
+    return createFileLineMsg(info->FileName, info->Line);
+
+  // If it failed, lookup again as a variable.
+  if (Optional<std::pair<std::string, unsigned>> fileLine =
+          file.getVariableLoc(sym.getName()))
+    return createFileLineMsg(fileLine->first, fileLine->second);
+
+  // File.sourceFile contains STT_FILE symbol, and that is a last resort.
+  return std::string(file.sourceFile);
+}
+
+std::string InputFile::getSrcMsg(const Symbol &sym, InputSectionBase &sec,
+                                 uint64_t offset) {
+  if (kind() != ObjKind)
+    return "";
+  switch (config->ekind) {
+  default:
+    llvm_unreachable("Invalid kind");
+  case ELF32LEKind:
+    return getSrcMsgAux(cast<ObjFile<ELF32LE>>(*this), sym, sec, offset);
+  case ELF32BEKind:
+    return getSrcMsgAux(cast<ObjFile<ELF32BE>>(*this), sym, sec, offset);
+  case ELF64LEKind:
+    return getSrcMsgAux(cast<ObjFile<ELF64LE>>(*this), sym, sec, offset);
+  case ELF64BEKind:
+    return getSrcMsgAux(cast<ObjFile<ELF64BE>>(*this), sym, sec, offset);
+  }
+}
+
+template <class ELFT> void ObjFile<ELFT>::initializeDwarf() {
+  dwarf = make<DWARFCache>(std::make_unique<DWARFContext>(
+      std::make_unique<LLDDwarfObj<ELFT>>(this)));
+}
+
+// Returns the pair of file name and line number describing location of data
+// object (variable, array, etc) definition.
+template <class ELFT>
+Optional<std::pair<std::string, unsigned>>
+ObjFile<ELFT>::getVariableLoc(StringRef name) {
+  llvm::call_once(initDwarfLine, [this]() { initializeDwarf(); });
+
+  return dwarf->getVariableLoc(name);
+}
+
+// Returns source line information for a given offset
+// using DWARF debug info.
+template <class ELFT>
+Optional<DILineInfo> ObjFile<ELFT>::getDILineInfo(InputSectionBase *s,
+                                                  uint64_t offset) {
+  llvm::call_once(initDwarfLine, [this]() { initializeDwarf(); });
+
+  // Detect SectionIndex for specified section.
+  uint64_t sectionIndex = object::SectionedAddress::UndefSection;
+  ArrayRef<InputSectionBase *> sections = s->file->getSections();
+  for (uint64_t curIndex = 0; curIndex < sections.size(); ++curIndex) {
+    if (s == sections[curIndex]) {
+      sectionIndex = curIndex;
+      break;
+    }
+  }
+
+  // Use fake address calculated by adding section file offset and offset in
+  // section. See comments for ObjectInfo class.
+  return dwarf->getDILineInfo(s->getOffsetInFile() + offset, sectionIndex);
+}
+
+ELFFileBase::ELFFileBase(Kind k, MemoryBufferRef mb) : InputFile(k, mb) {
+  ekind = getELFKind(mb, "");
+
+  switch (ekind) {
+  case ELF32LEKind:
+    init<ELF32LE>();
+    break;
+  case ELF32BEKind:
+    init<ELF32BE>();
+    break;
+  case ELF64LEKind:
+    init<ELF64LE>();
+    break;
+  case ELF64BEKind:
+    init<ELF64BE>();
+    break;
+  default:
+    llvm_unreachable("getELFKind");
+  }
+}
+
+template <typename Elf_Shdr>
+static const Elf_Shdr *findSection(ArrayRef<Elf_Shdr> sections, uint32_t type) {
+  for (const Elf_Shdr &sec : sections)
+    if (sec.sh_type == type)
+      return &sec;
+  return nullptr;
+}
+
+template <class ELFT> void ELFFileBase::init() {
+  using Elf_Shdr = typename ELFT::Shdr;
+  using Elf_Sym = typename ELFT::Sym;
+
+  // Initialize trivial attributes.
+  const ELFFile<ELFT> &obj = getObj<ELFT>();
+  emachine = obj.getHeader()->e_machine;
+  osabi = obj.getHeader()->e_ident[llvm::ELF::EI_OSABI];
+  abiVersion = obj.getHeader()->e_ident[llvm::ELF::EI_ABIVERSION];
+
+  ArrayRef<Elf_Shdr> sections = CHECK(obj.sections(), this);
+
+  // Find a symbol table.
+  bool isDSO =
+      (identify_magic(mb.getBuffer()) == file_magic::elf_shared_object);
+  const Elf_Shdr *symtabSec =
+      findSection(sections, isDSO ? SHT_DYNSYM : SHT_SYMTAB);
+
+  if (!symtabSec)
+    return;
+
+  // Initialize members corresponding to a symbol table.
+  firstGlobal = symtabSec->sh_info;
+
+  ArrayRef<Elf_Sym> eSyms = CHECK(obj.symbols(symtabSec), this);
+  if (firstGlobal == 0 || firstGlobal > eSyms.size())
+    fatal(toString(this) + ": invalid sh_info in symbol table");
+
+  elfSyms = reinterpret_cast<const void *>(eSyms.data());
+  numELFSyms = eSyms.size();
+  stringTable = CHECK(obj.getStringTableForSymtab(*symtabSec, sections), this);
+}
+
+template <class ELFT>
+uint32_t ObjFile<ELFT>::getSectionIndex(const Elf_Sym &sym) const {
+  return CHECK(
+      this->getObj().getSectionIndex(&sym, getELFSyms<ELFT>(), shndxTable),
+      this);
+}
+
+template <class ELFT> ArrayRef<Symbol *> ObjFile<ELFT>::getLocalSymbols() {
+  if (this->symbols.empty())
+    return {};
+  return makeArrayRef(this->symbols).slice(1, this->firstGlobal - 1);
+}
+
+template <class ELFT> ArrayRef<Symbol *> ObjFile<ELFT>::getGlobalSymbols() {
+  return makeArrayRef(this->symbols).slice(this->firstGlobal);
+}
+
+template <class ELFT> void ObjFile<ELFT>::parse(bool ignoreComdats) {
+  // Read a section table. justSymbols is usually false.
+  if (this->justSymbols)
+    initializeJustSymbols();
+  else
+    initializeSections(ignoreComdats);
+
+  // Read a symbol table.
+  initializeSymbols();
+}
+
+// Sections with SHT_GROUP and comdat bits define comdat section groups.
+// They are identified and deduplicated by group name. This function
+// returns a group name.
+template <class ELFT>
+StringRef ObjFile<ELFT>::getShtGroupSignature(ArrayRef<Elf_Shdr> sections,
+                                              const Elf_Shdr &sec) {
+  typename ELFT::SymRange symbols = this->getELFSyms<ELFT>();
+  if (sec.sh_info >= symbols.size())
+    fatal(toString(this) + ": invalid symbol index");
+  const typename ELFT::Sym &sym = symbols[sec.sh_info];
+  StringRef signature = CHECK(sym.getName(this->stringTable), this);
+
+  // As a special case, if a symbol is a section symbol and has no name,
+  // we use a section name as a signature.
+  //
+  // Such SHT_GROUP sections are invalid from the perspective of the ELF
+  // standard, but GNU gold 1.14 (the newest version as of July 2017) or
+  // older produce such sections as outputs for the -r option, so we need
+  // a bug-compatibility.
+  if (signature.empty() && sym.getType() == STT_SECTION)
+    return getSectionName(sec);
+  return signature;
+}
+
+template <class ELFT>
+bool ObjFile<ELFT>::shouldMerge(const Elf_Shdr &sec, StringRef name) {
+  // On a regular link we don't merge sections if -O0 (default is -O1). This
+  // sometimes makes the linker significantly faster, although the output will
+  // be bigger.
+  //
+  // Doing the same for -r would create a problem as it would combine sections
+  // with different sh_entsize. One option would be to just copy every SHF_MERGE
+  // section as is to the output. While this would produce a valid ELF file with
+  // usable SHF_MERGE sections, tools like (llvm-)?dwarfdump get confused when
+  // they see two .debug_str. We could have separate logic for combining
+  // SHF_MERGE sections based both on their name and sh_entsize, but that seems
+  // to be more trouble than it is worth. Instead, we just use the regular (-O1)
+  // logic for -r.
+  if (config->optimize == 0 && !config->relocatable)
+    return false;
+
+  // A mergeable section with size 0 is useless because they don't have
+  // any data to merge. A mergeable string section with size 0 can be
+  // argued as invalid because it doesn't end with a null character.
+  // We'll avoid a mess by handling them as if they were non-mergeable.
+  if (sec.sh_size == 0)
+    return false;
+
+  // Check for sh_entsize. The ELF spec is not clear about the zero
+  // sh_entsize. It says that "the member [sh_entsize] contains 0 if
+  // the section does not hold a table of fixed-size entries". We know
+  // that Rust 1.13 produces a string mergeable section with a zero
+  // sh_entsize. Here we just accept it rather than being picky about it.
+  uint64_t entSize = sec.sh_entsize;
+  if (entSize == 0)
+    return false;
+  if (sec.sh_size % entSize)
+    fatal(toString(this) + ":(" + name + "): SHF_MERGE section size (" +
+          Twine(sec.sh_size) + ") must be a multiple of sh_entsize (" +
+          Twine(entSize) + ")");
+
+  uint64_t flags = sec.sh_flags;
+  if (!(flags & SHF_MERGE))
+    return false;
+  if (flags & SHF_WRITE)
+    fatal(toString(this) + ":(" + name +
+          "): writable SHF_MERGE section is not supported");
+
+  return true;
+}
+
+// This is for --just-symbols.
+//
+// --just-symbols is a very minor feature that allows you to link your
+// output against other existing program, so that if you load both your
+// program and the other program into memory, your output can refer the
+// other program's symbols.
+//
+// When the option is given, we link "just symbols". The section table is
+// initialized with null pointers.
+template <class ELFT> void ObjFile<ELFT>::initializeJustSymbols() {
+  ArrayRef<Elf_Shdr> sections = CHECK(this->getObj().sections(), this);
+  this->sections.resize(sections.size());
+}
+
+// An ELF object file may contain a `.deplibs` section. If it exists, the
+// section contains a list of library specifiers such as `m` for libm. This
+// function resolves a given name by finding the first matching library checking
+// the various ways that a library can be specified to LLD. This ELF extension
+// is a form of autolinking and is called `dependent libraries`. It is currently
+// unique to LLVM and lld.
+static void addDependentLibrary(StringRef specifier, const InputFile *f) {
+  if (!config->dependentLibraries)
+    return;
+  if (fs::exists(specifier))
+    driver->addFile(specifier, /*withLOption=*/false);
+  else if (Optional<std::string> s = findFromSearchPaths(specifier))
+    driver->addFile(*s, /*withLOption=*/true);
+  else if (Optional<std::string> s = searchLibraryBaseName(specifier))
+    driver->addFile(*s, /*withLOption=*/true);
+  else
+    error(toString(f) +
+          ": unable to find library from dependent library specifier: " +
+          specifier);
+}
+
+// Record the membership of a section group so that in the garbage collection
+// pass, section group members are kept or discarded as a unit.
+template <class ELFT>
+static void handleSectionGroup(ArrayRef<InputSectionBase *> sections,
+                               ArrayRef<typename ELFT::Word> entries) {
+  bool hasAlloc = false;
+  for (uint32_t index : entries.slice(1)) {
+    if (index >= sections.size())
+      return;
+    if (InputSectionBase *s = sections[index])
+      if (s != &InputSection::discarded && s->flags & SHF_ALLOC)
+        hasAlloc = true;
+  }
+
+  // If any member has the SHF_ALLOC flag, the whole group is subject to garbage
+  // collection. See the comment in markLive(). This rule retains .debug_types
+  // and .rela.debug_types.
+  if (!hasAlloc)
+    return;
+
+  // Connect the members in a circular doubly-linked list via
+  // nextInSectionGroup.
+  InputSectionBase *head;
+  InputSectionBase *prev = nullptr;
+  for (uint32_t index : entries.slice(1)) {
+    InputSectionBase *s = sections[index];
+    if (!s || s == &InputSection::discarded)
+      continue;
+    if (prev)
+      prev->nextInSectionGroup = s;
+    else
+      head = s;
+    prev = s;
+  }
+  if (prev)
+    prev->nextInSectionGroup = head;
+}
+
+template <class ELFT>
+void ObjFile<ELFT>::initializeSections(bool ignoreComdats) {
+  const ELFFile<ELFT> &obj = this->getObj();
+
+  ArrayRef<Elf_Shdr> objSections = CHECK(obj.sections(), this);
+  uint64_t size = objSections.size();
+  this->sections.resize(size);
+  this->sectionStringTable =
+      CHECK(obj.getSectionStringTable(objSections), this);
+
+  std::vector<ArrayRef<Elf_Word>> selectedGroups;
+
+  for (size_t i = 0, e = objSections.size(); i < e; ++i) {
+    if (this->sections[i] == &InputSection::discarded)
+      continue;
+    const Elf_Shdr &sec = objSections[i];
+
+    if (sec.sh_type == ELF::SHT_LLVM_CALL_GRAPH_PROFILE)
+      cgProfile =
+          check(obj.template getSectionContentsAsArray<Elf_CGProfile>(&sec));
+
+    // SHF_EXCLUDE'ed sections are discarded by the linker. However,
+    // if -r is given, we'll let the final link discard such sections.
+    // This is compatible with GNU.
+    if ((sec.sh_flags & SHF_EXCLUDE) && !config->relocatable) {
+      if (sec.sh_type == SHT_LLVM_ADDRSIG) {
+        // We ignore the address-significance table if we know that the object
+        // file was created by objcopy or ld -r. This is because these tools
+        // will reorder the symbols in the symbol table, invalidating the data
+        // in the address-significance table, which refers to symbols by index.
+        if (sec.sh_link != 0)
+          this->addrsigSec = &sec;
+        else if (config->icf == ICFLevel::Safe)
+          warn(toString(this) + ": --icf=safe is incompatible with object "
+                                "files created using objcopy or ld -r");
+      }
+      this->sections[i] = &InputSection::discarded;
+      continue;
+    }
+
+    switch (sec.sh_type) {
+    case SHT_GROUP: {
+      // De-duplicate section groups by their signatures.
+      StringRef signature = getShtGroupSignature(objSections, sec);
+      this->sections[i] = &InputSection::discarded;
+
+
+      ArrayRef<Elf_Word> entries =
+          CHECK(obj.template getSectionContentsAsArray<Elf_Word>(&sec), this);
+      if (entries.empty())
+        fatal(toString(this) + ": empty SHT_GROUP");
+
+      // The first word of a SHT_GROUP section contains flags. Currently,
+      // the standard defines only "GRP_COMDAT" flag for the COMDAT group.
+      // An group with the empty flag doesn't define anything; such sections
+      // are just skipped.
+      if (entries[0] == 0)
+        continue;
+
+      if (entries[0] != GRP_COMDAT)
+        fatal(toString(this) + ": unsupported SHT_GROUP format");
+
+      bool isNew =
+          ignoreComdats ||
+          symtab->comdatGroups.try_emplace(CachedHashStringRef(signature), this)
+              .second;
+      if (isNew) {
+        if (config->relocatable)
+          this->sections[i] = createInputSection(sec);
+        selectedGroups.push_back(entries);
+        continue;
+      }
+
+      // Otherwise, discard group members.
+      for (uint32_t secIndex : entries.slice(1)) {
+        if (secIndex >= size)
+          fatal(toString(this) +
+                ": invalid section index in group: " + Twine(secIndex));
+        this->sections[secIndex] = &InputSection::discarded;
+      }
+      break;
+    }
+    case SHT_SYMTAB_SHNDX:
+      shndxTable = CHECK(obj.getSHNDXTable(sec, objSections), this);
+      break;
+    case SHT_SYMTAB:
+    case SHT_STRTAB:
+    case SHT_NULL:
+      break;
+    default:
+      this->sections[i] = createInputSection(sec);
+    }
+  }
+
+  // This block handles SHF_LINK_ORDER.
+  for (size_t i = 0, e = objSections.size(); i < e; ++i) {
+    if (this->sections[i] == &InputSection::discarded)
+      continue;
+    const Elf_Shdr &sec = objSections[i];
+    if (!(sec.sh_flags & SHF_LINK_ORDER))
+      continue;
+
+    // .ARM.exidx sections have a reverse dependency on the InputSection they
+    // have a SHF_LINK_ORDER dependency, this is identified by the sh_link.
+    InputSectionBase *linkSec = nullptr;
+    if (sec.sh_link < this->sections.size())
+      linkSec = this->sections[sec.sh_link];
+    if (!linkSec)
+      fatal(toString(this) + ": invalid sh_link index: " + Twine(sec.sh_link));
+
+    InputSection *isec = cast<InputSection>(this->sections[i]);
+    linkSec->dependentSections.push_back(isec);
+    if (!isa<InputSection>(linkSec))
+      error("a section " + isec->name +
+            " with SHF_LINK_ORDER should not refer a non-regular section: " +
+            toString(linkSec));
+  }
+
+  for (ArrayRef<Elf_Word> entries : selectedGroups)
+    handleSectionGroup<ELFT>(this->sections, entries);
+}
+
+// For ARM only, to set the EF_ARM_ABI_FLOAT_SOFT or EF_ARM_ABI_FLOAT_HARD
+// flag in the ELF Header we need to look at Tag_ABI_VFP_args to find out how
+// the input objects have been compiled.
+static void updateARMVFPArgs(const ARMAttributeParser &attributes,
+                             const InputFile *f) {
+  if (!attributes.hasAttribute(ARMBuildAttrs::ABI_VFP_args))
+    // If an ABI tag isn't present then it is implicitly given the value of 0
+    // which maps to ARMBuildAttrs::BaseAAPCS. However many assembler files,
+    // including some in glibc that don't use FP args (and should have value 3)
+    // don't have the attribute so we do not consider an implicit value of 0
+    // as a clash.
+    return;
+
+  unsigned vfpArgs = attributes.getAttributeValue(ARMBuildAttrs::ABI_VFP_args);
+  ARMVFPArgKind arg;
+  switch (vfpArgs) {
+  case ARMBuildAttrs::BaseAAPCS:
+    arg = ARMVFPArgKind::Base;
+    break;
+  case ARMBuildAttrs::HardFPAAPCS:
+    arg = ARMVFPArgKind::VFP;
+    break;
+  case ARMBuildAttrs::ToolChainFPPCS:
+    // Tool chain specific convention that conforms to neither AAPCS variant.
+    arg = ARMVFPArgKind::ToolChain;
+    break;
+  case ARMBuildAttrs::CompatibleFPAAPCS:
+    // Object compatible with all conventions.
+    return;
+  default:
+    error(toString(f) + ": unknown Tag_ABI_VFP_args value: " + Twine(vfpArgs));
+    return;
+  }
+  // Follow ld.bfd and error if there is a mix of calling conventions.
+  if (config->armVFPArgs != arg && config->armVFPArgs != ARMVFPArgKind::Default)
+    error(toString(f) + ": incompatible Tag_ABI_VFP_args");
+  else
+    config->armVFPArgs = arg;
+}
+
+// The ARM support in lld makes some use of instructions that are not available
+// on all ARM architectures. Namely:
+// - Use of BLX instruction for interworking between ARM and Thumb state.
+// - Use of the extended Thumb branch encoding in relocation.
+// - Use of the MOVT/MOVW instructions in Thumb Thunks.
+// The ARM Attributes section contains information about the architecture chosen
+// at compile time. We follow the convention that if at least one input object
+// is compiled with an architecture that supports these features then lld is
+// permitted to use them.
+static void updateSupportedARMFeatures(const ARMAttributeParser &attributes) {
+  if (!attributes.hasAttribute(ARMBuildAttrs::CPU_arch))
+    return;
+  auto arch = attributes.getAttributeValue(ARMBuildAttrs::CPU_arch);
+  switch (arch) {
+  case ARMBuildAttrs::Pre_v4:
+  case ARMBuildAttrs::v4:
+  case ARMBuildAttrs::v4T:
+    // Architectures prior to v5 do not support BLX instruction
+    break;
+  case ARMBuildAttrs::v5T:
+  case ARMBuildAttrs::v5TE:
+  case ARMBuildAttrs::v5TEJ:
+  case ARMBuildAttrs::v6:
+  case ARMBuildAttrs::v6KZ:
+  case ARMBuildAttrs::v6K:
+    config->armHasBlx = true;
+    // Architectures used in pre-Cortex processors do not support
+    // The J1 = 1 J2 = 1 Thumb branch range extension, with the exception
+    // of Architecture v6T2 (arm1156t2-s and arm1156t2f-s) that do.
+    break;
+  default:
+    // All other Architectures have BLX and extended branch encoding
+    config->armHasBlx = true;
+    config->armJ1J2BranchEncoding = true;
+    if (arch != ARMBuildAttrs::v6_M && arch != ARMBuildAttrs::v6S_M)
+      // All Architectures used in Cortex processors with the exception
+      // of v6-M and v6S-M have the MOVT and MOVW instructions.
+      config->armHasMovtMovw = true;
+    break;
+  }
+}
+
+// If a source file is compiled with x86 hardware-assisted call flow control
+// enabled, the generated object file contains feature flags indicating that
+// fact. This function reads the feature flags and returns it.
+//
+// Essentially we want to read a single 32-bit value in this function, but this
+// function is rather complicated because the value is buried deep inside a
+// .note.gnu.property section.
+//
+// The section consists of one or more NOTE records. Each NOTE record consists
+// of zero or more type-length-value fields. We want to find a field of a
+// certain type. It seems a bit too much to just store a 32-bit value, perhaps
+// the ABI is unnecessarily complicated.
+template <class ELFT>
+static uint32_t readAndFeatures(ObjFile<ELFT> *obj, ArrayRef<uint8_t> data) {
+  using Elf_Nhdr = typename ELFT::Nhdr;
+  using Elf_Note = typename ELFT::Note;
+
+  uint32_t featuresSet = 0;
+  while (!data.empty()) {
+    // Read one NOTE record.
+    if (data.size() < sizeof(Elf_Nhdr))
+      fatal(toString(obj) + ": .note.gnu.property: section too short");
+
+    auto *nhdr = reinterpret_cast<const Elf_Nhdr *>(data.data());
+    if (data.size() < nhdr->getSize())
+      fatal(toString(obj) + ": .note.gnu.property: section too short");
+
+    Elf_Note note(*nhdr);
+    if (nhdr->n_type != NT_GNU_PROPERTY_TYPE_0 || note.getName() != "GNU") {
+      data = data.slice(nhdr->getSize());
+      continue;
+    }
+
+    uint32_t featureAndType = config->emachine == EM_AARCH64
+                                  ? GNU_PROPERTY_AARCH64_FEATURE_1_AND
+                                  : GNU_PROPERTY_X86_FEATURE_1_AND;
+
+    // Read a body of a NOTE record, which consists of type-length-value fields.
+    ArrayRef<uint8_t> desc = note.getDesc();
+    while (!desc.empty()) {
+      if (desc.size() < 8)
+        fatal(toString(obj) + ": .note.gnu.property: section too short");
+
+      uint32_t type = read32le(desc.data());
+      uint32_t size = read32le(desc.data() + 4);
+
+      if (type == featureAndType) {
+        // We found a FEATURE_1_AND field. There may be more than one of these
+        // in a .note.gnu.property section, for a relocatable object we
+        // accumulate the bits set.
+        featuresSet |= read32le(desc.data() + 8);
+      }
+
+      // On 64-bit, a payload may be followed by a 4-byte padding to make its
+      // size a multiple of 8.
+      if (ELFT::Is64Bits)
+        size = alignTo(size, 8);
+
+      desc = desc.slice(size + 8); // +8 for Type and Size
+    }
+
+    // Go to next NOTE record to look for more FEATURE_1_AND descriptions.
+    data = data.slice(nhdr->getSize());
+  }
+
+  return featuresSet;
+}
+
+template <class ELFT>
+InputSectionBase *ObjFile<ELFT>::getRelocTarget(const Elf_Shdr &sec) {
+  uint32_t idx = sec.sh_info;
+  if (idx >= this->sections.size())
+    fatal(toString(this) + ": invalid relocated section index: " + Twine(idx));
+  InputSectionBase *target = this->sections[idx];
+
+  // Strictly speaking, a relocation section must be included in the
+  // group of the section it relocates. However, LLVM 3.3 and earlier
+  // would fail to do so, so we gracefully handle that case.
+  if (target == &InputSection::discarded)
+    return nullptr;
+
+  if (!target)
+    fatal(toString(this) + ": unsupported relocation reference");
+  return target;
+}
+
+// Create a regular InputSection class that has the same contents
+// as a given section.
+static InputSection *toRegularSection(MergeInputSection *sec) {
+  return make<InputSection>(sec->file, sec->flags, sec->type, sec->alignment,
+                            sec->data(), sec->name);
+}
+
+template <class ELFT>
+InputSectionBase *ObjFile<ELFT>::createInputSection(const Elf_Shdr &sec) {
+  StringRef name = getSectionName(sec);
+
+  switch (sec.sh_type) {
+  case SHT_ARM_ATTRIBUTES: {
+    if (config->emachine != EM_ARM)
+      break;
+    ARMAttributeParser attributes;
+    ArrayRef<uint8_t> contents = check(this->getObj().getSectionContents(&sec));
+    attributes.Parse(contents, /*isLittle*/ config->ekind == ELF32LEKind);
+    updateSupportedARMFeatures(attributes);
+    updateARMVFPArgs(attributes, this);
+
+    // FIXME: Retain the first attribute section we see. The eglibc ARM
+    // dynamic loaders require the presence of an attribute section for dlopen
+    // to work. In a full implementation we would merge all attribute sections.
+    if (in.armAttributes == nullptr) {
+      in.armAttributes = make<InputSection>(*this, sec, name);
+      return in.armAttributes;
+    }
+    return &InputSection::discarded;
+  }
+  case SHT_LLVM_DEPENDENT_LIBRARIES: {
+    if (config->relocatable)
+      break;
+    ArrayRef<char> data =
+        CHECK(this->getObj().template getSectionContentsAsArray<char>(&sec), this);
+    if (!data.empty() && data.back() != '\0') {
+      error(toString(this) +
+            ": corrupted dependent libraries section (unterminated string): " +
+            name);
+      return &InputSection::discarded;
+    }
+    for (const char *d = data.begin(), *e = data.end(); d < e;) {
+      StringRef s(d);
+      addDependentLibrary(s, this);
+      d += s.size() + 1;
+    }
+    return &InputSection::discarded;
+  }
+  case SHT_RELA:
+  case SHT_REL: {
+    // Find a relocation target section and associate this section with that.
+    // Target may have been discarded if it is in a different section group
+    // and the group is discarded, even though it's a violation of the
+    // spec. We handle that situation gracefully by discarding dangling
+    // relocation sections.
+    InputSectionBase *target = getRelocTarget(sec);
+    if (!target)
+      return nullptr;
+
+    // ELF spec allows mergeable sections with relocations, but they are
+    // rare, and it is in practice hard to merge such sections by contents,
+    // because applying relocations at end of linking changes section
+    // contents. So, we simply handle such sections as non-mergeable ones.
+    // Degrading like this is acceptable because section merging is optional.
+    if (auto *ms = dyn_cast<MergeInputSection>(target)) {
+      target = toRegularSection(ms);
+      this->sections[sec.sh_info] = target;
+    }
+
+    // This section contains relocation information.
+    // If -r is given, we do not interpret or apply relocation
+    // but just copy relocation sections to output.
+    if (config->relocatable) {
+      InputSection *relocSec = make<InputSection>(*this, sec, name);
+      // We want to add a dependency to target, similar like we do for
+      // -emit-relocs below. This is useful for the case when linker script
+      // contains the "/DISCARD/". It is perhaps uncommon to use a script with
+      // -r, but we faced it in the Linux kernel and have to handle such case
+      // and not to crash.
+      target->dependentSections.push_back(relocSec);
+      return relocSec;
+    }
+
+    if (target->firstRelocation)
+      fatal(toString(this) +
+            ": multiple relocation sections to one section are not supported");
+
+    if (sec.sh_type == SHT_RELA) {
+      ArrayRef<Elf_Rela> rels = CHECK(getObj().relas(&sec), this);
+      target->firstRelocation = rels.begin();
+      target->numRelocations = rels.size();
+      target->areRelocsRela = true;
+    } else {
+      ArrayRef<Elf_Rel> rels = CHECK(getObj().rels(&sec), this);
+      target->firstRelocation = rels.begin();
+      target->numRelocations = rels.size();
+      target->areRelocsRela = false;
+    }
+    assert(isUInt<31>(target->numRelocations));
+
+    // Relocation sections processed by the linker are usually removed
+    // from the output, so returning `nullptr` for the normal case.
+    // However, if -emit-relocs is given, we need to leave them in the output.
+    // (Some post link analysis tools need this information.)
+    if (config->emitRelocs) {
+      InputSection *relocSec = make<InputSection>(*this, sec, name);
+      // We will not emit relocation section if target was discarded.
+      target->dependentSections.push_back(relocSec);
+      return relocSec;
+    }
+    return nullptr;
+  }
+  }
+
+  // The GNU linker uses .note.GNU-stack section as a marker indicating
+  // that the code in the object file does not expect that the stack is
+  // executable (in terms of NX bit). If all input files have the marker,
+  // the GNU linker adds a PT_GNU_STACK segment to tells the loader to
+  // make the stack non-executable. Most object files have this section as
+  // of 2017.
+  //
+  // But making the stack non-executable is a norm today for security
+  // reasons. Failure to do so may result in a serious security issue.
+  // Therefore, we make LLD always add PT_GNU_STACK unless it is
+  // explicitly told to do otherwise (by -z execstack). Because the stack
+  // executable-ness is controlled solely by command line options,
+  // .note.GNU-stack sections are simply ignored.
+  if (name == ".note.GNU-stack")
+    return &InputSection::discarded;
+
+  // Object files that use processor features such as Intel Control-Flow
+  // Enforcement (CET) or AArch64 Branch Target Identification BTI, use a
+  // .note.gnu.property section containing a bitfield of feature bits like the
+  // GNU_PROPERTY_X86_FEATURE_1_IBT flag. Read a bitmap containing the flag.
+  //
+  // Since we merge bitmaps from multiple object files to create a new
+  // .note.gnu.property containing a single AND'ed bitmap, we discard an input
+  // file's .note.gnu.property section.
+  if (name == ".note.gnu.property") {
+    ArrayRef<uint8_t> contents = check(this->getObj().getSectionContents(&sec));
+    this->andFeatures = readAndFeatures(this, contents);
+    return &InputSection::discarded;
+  }
+
+  // Split stacks is a feature to support a discontiguous stack,
+  // commonly used in the programming language Go. For the details,
+  // see https://gcc.gnu.org/wiki/SplitStacks. An object file compiled
+  // for split stack will include a .note.GNU-split-stack section.
+  if (name == ".note.GNU-split-stack") {
+    if (config->relocatable) {
+      error("cannot mix split-stack and non-split-stack in a relocatable link");
+      return &InputSection::discarded;
+    }
+    this->splitStack = true;
+    return &InputSection::discarded;
+  }
+
+  // An object file cmpiled for split stack, but where some of the
+  // functions were compiled with the no_split_stack_attribute will
+  // include a .note.GNU-no-split-stack section.
+  if (name == ".note.GNU-no-split-stack") {
+    this->someNoSplitStack = true;
+    return &InputSection::discarded;
+  }
+
+  // The linkonce feature is a sort of proto-comdat. Some glibc i386 object
+  // files contain definitions of symbol "__x86.get_pc_thunk.bx" in linkonce
+  // sections. Drop those sections to avoid duplicate symbol errors.
+  // FIXME: This is glibc PR20543, we should remove this hack once that has been
+  // fixed for a while.
+  if (name == ".gnu.linkonce.t.__x86.get_pc_thunk.bx" ||
+      name == ".gnu.linkonce.t.__i686.get_pc_thunk.bx")
+    return &InputSection::discarded;
+
+  // If we are creating a new .build-id section, strip existing .build-id
+  // sections so that the output won't have more than one .build-id.
+  // This is not usually a problem because input object files normally don't
+  // have .build-id sections, but you can create such files by
+  // "ld.{bfd,gold,lld} -r --build-id", and we want to guard against it.
+  if (name == ".note.gnu.build-id" && config->buildId != BuildIdKind::None)
+    return &InputSection::discarded;
+
+  // The linker merges EH (exception handling) frames and creates a
+  // .eh_frame_hdr section for runtime. So we handle them with a special
+  // class. For relocatable outputs, they are just passed through.
+  if (name == ".eh_frame" && !config->relocatable)
+    return make<EhInputSection>(*this, sec, name);
+
+  if (shouldMerge(sec, name))
+    return make<MergeInputSection>(*this, sec, name);
+  return make<InputSection>(*this, sec, name);
+}
+
+template <class ELFT>
+StringRef ObjFile<ELFT>::getSectionName(const Elf_Shdr &sec) {
+  return CHECK(getObj().getSectionName(&sec, sectionStringTable), this);
+}
+
+// Initialize this->Symbols. this->Symbols is a parallel array as
+// its corresponding ELF symbol table.
+template <class ELFT> void ObjFile<ELFT>::initializeSymbols() {
+  ArrayRef<Elf_Sym> eSyms = this->getELFSyms<ELFT>();
+  this->symbols.resize(eSyms.size());
+
+  // Our symbol table may have already been partially initialized
+  // because of LazyObjFile.
+  for (size_t i = 0, end = eSyms.size(); i != end; ++i)
+    if (!this->symbols[i] && eSyms[i].getBinding() != STB_LOCAL)
+      this->symbols[i] =
+          symtab->insert(CHECK(eSyms[i].getName(this->stringTable), this));
+
+  // Fill this->Symbols. A symbol is either local or global.
+  for (size_t i = 0, end = eSyms.size(); i != end; ++i) {
+    const Elf_Sym &eSym = eSyms[i];
+
+    // Read symbol attributes.
+    uint32_t secIdx = getSectionIndex(eSym);
+    if (secIdx >= this->sections.size())
+      fatal(toString(this) + ": invalid section index: " + Twine(secIdx));
+
+    InputSectionBase *sec = this->sections[secIdx];
+    uint8_t binding = eSym.getBinding();
+    uint8_t stOther = eSym.st_other;
+    uint8_t type = eSym.getType();
+    uint64_t value = eSym.st_value;
+    uint64_t size = eSym.st_size;
+    StringRefZ name = this->stringTable.data() + eSym.st_name;
+
+    // Handle local symbols. Local symbols are not added to the symbol
+    // table because they are not visible from other object files. We
+    // allocate symbol instances and add their pointers to Symbols.
+    if (binding == STB_LOCAL) {
+      if (eSym.getType() == STT_FILE)
+        sourceFile = CHECK(eSym.getName(this->stringTable), this);
+
+      if (this->stringTable.size() <= eSym.st_name)
+        fatal(toString(this) + ": invalid symbol name offset");
+
+      if (eSym.st_shndx == SHN_UNDEF)
+        this->symbols[i] = make<Undefined>(this, name, binding, stOther, type);
+      else if (sec == &InputSection::discarded)
+        this->symbols[i] = make<Undefined>(this, name, binding, stOther, type,
+                                           /*DiscardedSecIdx=*/secIdx);
+      else
+        this->symbols[i] =
+            make<Defined>(this, name, binding, stOther, type, value, size, sec);
+      continue;
+    }
+
+    // Handle global undefined symbols.
+    if (eSym.st_shndx == SHN_UNDEF) {
+      this->symbols[i]->resolve(Undefined{this, name, binding, stOther, type});
+      this->symbols[i]->referenced = true;
+      continue;
+    }
+
+    // Handle global common symbols.
+    if (eSym.st_shndx == SHN_COMMON) {
+      if (value == 0 || value >= UINT32_MAX)
+        fatal(toString(this) + ": common symbol '" + StringRef(name.data) +
+              "' has invalid alignment: " + Twine(value));
+      this->symbols[i]->resolve(
+          CommonSymbol{this, name, binding, stOther, type, value, size});
+      continue;
+    }
+
+    // If a defined symbol is in a discarded section, handle it as if it
+    // were an undefined symbol. Such symbol doesn't comply with the
+    // standard, but in practice, a .eh_frame often directly refer
+    // COMDAT member sections, and if a comdat group is discarded, some
+    // defined symbol in a .eh_frame becomes dangling symbols.
+    if (sec == &InputSection::discarded) {
+      this->symbols[i]->resolve(
+          Undefined{this, name, binding, stOther, type, secIdx});
+      continue;
+    }
+
+    // Handle global defined symbols.
+    if (binding == STB_GLOBAL || binding == STB_WEAK ||
+        binding == STB_GNU_UNIQUE) {
+      this->symbols[i]->resolve(
+          Defined{this, name, binding, stOther, type, value, size, sec});
+      continue;
+    }
+
+    fatal(toString(this) + ": unexpected binding: " + Twine((int)binding));
+  }
+}
+
+ArchiveFile::ArchiveFile(std::unique_ptr<Archive> &&file)
+    : InputFile(ArchiveKind, file->getMemoryBufferRef()),
+      file(std::move(file)) {}
+
+void ArchiveFile::parse() {
+  for (const Archive::Symbol &sym : file->symbols())
+    symtab->addSymbol(LazyArchive{*this, sym});
+}
+
+// Returns a buffer pointing to a member file containing a given symbol.
+void ArchiveFile::fetch(const Archive::Symbol &sym) {
+  Archive::Child c =
+      CHECK(sym.getMember(), toString(this) +
+                                 ": could not get the member for symbol " +
+                                 toELFString(sym));
+
+  if (!seen.insert(c.getChildOffset()).second)
+    return;
+
+  MemoryBufferRef mb =
+      CHECK(c.getMemoryBufferRef(),
+            toString(this) +
+                ": could not get the buffer for the member defining symbol " +
+                toELFString(sym));
+
+  if (tar && c.getParent()->isThin())
+    tar->append(relativeToRoot(CHECK(c.getFullName(), this)), mb.getBuffer());
+
+  InputFile *file = createObjectFile(
+      mb, getName(), c.getParent()->isThin() ? 0 : c.getChildOffset());
+  file->groupId = groupId;
+  parseFile(file);
+}
+
+unsigned SharedFile::vernauxNum;
+
+// Parse the version definitions in the object file if present, and return a
+// vector whose nth element contains a pointer to the Elf_Verdef for version
+// identifier n. Version identifiers that are not definitions map to nullptr.
+template <typename ELFT>
+static std::vector<const void *> parseVerdefs(const uint8_t *base,
+                                              const typename ELFT::Shdr *sec) {
+  if (!sec)
+    return {};
+
+  // We cannot determine the largest verdef identifier without inspecting
+  // every Elf_Verdef, but both bfd and gold assign verdef identifiers
+  // sequentially starting from 1, so we predict that the largest identifier
+  // will be verdefCount.
+  unsigned verdefCount = sec->sh_info;
+  std::vector<const void *> verdefs(verdefCount + 1);
+
+  // Build the Verdefs array by following the chain of Elf_Verdef objects
+  // from the start of the .gnu.version_d section.
+  const uint8_t *verdef = base + sec->sh_offset;
+  for (unsigned i = 0; i != verdefCount; ++i) {
+    auto *curVerdef = reinterpret_cast<const typename ELFT::Verdef *>(verdef);
+    verdef += curVerdef->vd_next;
+    unsigned verdefIndex = curVerdef->vd_ndx;
+    verdefs.resize(verdefIndex + 1);
+    verdefs[verdefIndex] = curVerdef;
+  }
+  return verdefs;
+}
+
+// We do not usually care about alignments of data in shared object
+// files because the loader takes care of it. However, if we promote a
+// DSO symbol to point to .bss due to copy relocation, we need to keep
+// the original alignment requirements. We infer it in this function.
+template <typename ELFT>
+static uint64_t getAlignment(ArrayRef<typename ELFT::Shdr> sections,
+                             const typename ELFT::Sym &sym) {
+  uint64_t ret = UINT64_MAX;
+  if (sym.st_value)
+    ret = 1ULL << countTrailingZeros((uint64_t)sym.st_value);
+  if (0 < sym.st_shndx && sym.st_shndx < sections.size())
+    ret = std::min<uint64_t>(ret, sections[sym.st_shndx].sh_addralign);
+  return (ret > UINT32_MAX) ? 0 : ret;
+}
+
+// Fully parse the shared object file.
+//
+// This function parses symbol versions. If a DSO has version information,
+// the file has a ".gnu.version_d" section which contains symbol version
+// definitions. Each symbol is associated to one version through a table in
+// ".gnu.version" section. That table is a parallel array for the symbol
+// table, and each table entry contains an index in ".gnu.version_d".
+//
+// The special index 0 is reserved for VERF_NDX_LOCAL and 1 is for
+// VER_NDX_GLOBAL. There's no table entry for these special versions in
+// ".gnu.version_d".
+//
+// The file format for symbol versioning is perhaps a bit more complicated
+// than necessary, but you can easily understand the code if you wrap your
+// head around the data structure described above.
+template <class ELFT> void SharedFile::parse() {
+  using Elf_Dyn = typename ELFT::Dyn;
+  using Elf_Shdr = typename ELFT::Shdr;
+  using Elf_Sym = typename ELFT::Sym;
+  using Elf_Verdef = typename ELFT::Verdef;
+  using Elf_Versym = typename ELFT::Versym;
+
+  ArrayRef<Elf_Dyn> dynamicTags;
+  const ELFFile<ELFT> obj = this->getObj<ELFT>();
+  ArrayRef<Elf_Shdr> sections = CHECK(obj.sections(), this);
+
+  const Elf_Shdr *versymSec = nullptr;
+  const Elf_Shdr *verdefSec = nullptr;
+
+  // Search for .dynsym, .dynamic, .symtab, .gnu.version and .gnu.version_d.
+  for (const Elf_Shdr &sec : sections) {
+    switch (sec.sh_type) {
+    default:
+      continue;
+    case SHT_DYNAMIC:
+      dynamicTags =
+          CHECK(obj.template getSectionContentsAsArray<Elf_Dyn>(&sec), this);
+      break;
+    case SHT_GNU_versym:
+      versymSec = &sec;
+      break;
+    case SHT_GNU_verdef:
+      verdefSec = &sec;
+      break;
+    }
+  }
+
+  if (versymSec && numELFSyms == 0) {
+    error("SHT_GNU_versym should be associated with symbol table");
+    return;
+  }
+
+  // Search for a DT_SONAME tag to initialize this->soName.
+  for (const Elf_Dyn &dyn : dynamicTags) {
+    if (dyn.d_tag == DT_NEEDED) {
+      uint64_t val = dyn.getVal();
+      if (val >= this->stringTable.size())
+        fatal(toString(this) + ": invalid DT_NEEDED entry");
+      dtNeeded.push_back(this->stringTable.data() + val);
+    } else if (dyn.d_tag == DT_SONAME) {
+      uint64_t val = dyn.getVal();
+      if (val >= this->stringTable.size())
+        fatal(toString(this) + ": invalid DT_SONAME entry");
+      soName = this->stringTable.data() + val;
+    }
+  }
+
+  // DSOs are uniquified not by filename but by soname.
+  DenseMap<StringRef, SharedFile *>::iterator it;
+  bool wasInserted;
+  std::tie(it, wasInserted) = symtab->soNames.try_emplace(soName, this);
+
+  // If a DSO appears more than once on the command line with and without
+  // --as-needed, --no-as-needed takes precedence over --as-needed because a
+  // user can add an extra DSO with --no-as-needed to force it to be added to
+  // the dependency list.
+  it->second->isNeeded |= isNeeded;
+  if (!wasInserted)
+    return;
+
+  sharedFiles.push_back(this);
+
+  verdefs = parseVerdefs<ELFT>(obj.base(), verdefSec);
+
+  // Parse ".gnu.version" section which is a parallel array for the symbol
+  // table. If a given file doesn't have a ".gnu.version" section, we use
+  // VER_NDX_GLOBAL.
+  size_t size = numELFSyms - firstGlobal;
+  std::vector<uint32_t> versyms(size, VER_NDX_GLOBAL);
+  if (versymSec) {
+    ArrayRef<Elf_Versym> versym =
+        CHECK(obj.template getSectionContentsAsArray<Elf_Versym>(versymSec),
+              this)
+            .slice(firstGlobal);
+    for (size_t i = 0; i < size; ++i)
+      versyms[i] = versym[i].vs_index;
+  }
+
+  // System libraries can have a lot of symbols with versions. Using a
+  // fixed buffer for computing the versions name (foo@ver) can save a
+  // lot of allocations.
+  SmallString<0> versionedNameBuffer;
+
+  // Add symbols to the symbol table.
+  ArrayRef<Elf_Sym> syms = this->getGlobalELFSyms<ELFT>();
+  for (size_t i = 0; i < syms.size(); ++i) {
+    const Elf_Sym &sym = syms[i];
+
+    // ELF spec requires that all local symbols precede weak or global
+    // symbols in each symbol table, and the index of first non-local symbol
+    // is stored to sh_info. If a local symbol appears after some non-local
+    // symbol, that's a violation of the spec.
+    StringRef name = CHECK(sym.getName(this->stringTable), this);
+    if (sym.getBinding() == STB_LOCAL) {
+      warn("found local symbol '" + name +
+           "' in global part of symbol table in file " + toString(this));
+      continue;
+    }
+
+    if (sym.isUndefined()) {
+      Symbol *s = symtab->addSymbol(
+          Undefined{this, name, sym.getBinding(), sym.st_other, sym.getType()});
+      s->exportDynamic = true;
+      continue;
+    }
+
+    // MIPS BFD linker puts _gp_disp symbol into DSO files and incorrectly
+    // assigns VER_NDX_LOCAL to this section global symbol. Here is a
+    // workaround for this bug.
+    uint32_t idx = versyms[i] & ~VERSYM_HIDDEN;
+    if (config->emachine == EM_MIPS && idx == VER_NDX_LOCAL &&
+        name == "_gp_disp")
+      continue;
+
+    uint32_t alignment = getAlignment<ELFT>(sections, sym);
+    if (!(versyms[i] & VERSYM_HIDDEN)) {
+      symtab->addSymbol(SharedSymbol{*this, name, sym.getBinding(),
+                                     sym.st_other, sym.getType(), sym.st_value,
+                                     sym.st_size, alignment, idx});
+    }
+
+    // Also add the symbol with the versioned name to handle undefined symbols
+    // with explicit versions.
+    if (idx == VER_NDX_GLOBAL)
+      continue;
+
+    if (idx >= verdefs.size() || idx == VER_NDX_LOCAL) {
+      error("corrupt input file: version definition index " + Twine(idx) +
+            " for symbol " + name + " is out of bounds\n>>> defined in " +
+            toString(this));
+      continue;
+    }
+
+    StringRef verName =
+        this->stringTable.data() +
+        reinterpret_cast<const Elf_Verdef *>(verdefs[idx])->getAux()->vda_name;
+    versionedNameBuffer.clear();
+    name = (name + "@" + verName).toStringRef(versionedNameBuffer);
+    symtab->addSymbol(SharedSymbol{*this, saver.save(name), sym.getBinding(),
+                                   sym.st_other, sym.getType(), sym.st_value,
+                                   sym.st_size, alignment, idx});
+  }
+}
+
+static ELFKind getBitcodeELFKind(const Triple &t) {
+  if (t.isLittleEndian())
+    return t.isArch64Bit() ? ELF64LEKind : ELF32LEKind;
+  return t.isArch64Bit() ? ELF64BEKind : ELF32BEKind;
+}
+
+static uint8_t getBitcodeMachineKind(StringRef path, const Triple &t) {
+  switch (t.getArch()) {
+  case Triple::aarch64:
+    return EM_AARCH64;
+  case Triple::amdgcn:
+  case Triple::r600:
+    return EM_AMDGPU;
+  case Triple::arm:
+  case Triple::thumb:
+    return EM_ARM;
+  case Triple::avr:
+    return EM_AVR;
+  case Triple::mips:
+  case Triple::mipsel:
+  case Triple::mips64:
+  case Triple::mips64el:
+    return EM_MIPS;
+  case Triple::msp430:
+    return EM_MSP430;
+  case Triple::ppc:
+    return EM_PPC;
+  case Triple::ppc64:
+  case Triple::ppc64le:
+    return EM_PPC64;
+  case Triple::riscv32:
+  case Triple::riscv64:
+    return EM_RISCV;
+  case Triple::x86:
+    return t.isOSIAMCU() ? EM_IAMCU : EM_386;
+  case Triple::x86_64:
+    return EM_X86_64;
+  default:
+    error(path + ": could not infer e_machine from bitcode target triple " +
+          t.str());
+    return EM_NONE;
+  }
+}
+
+BitcodeFile::BitcodeFile(MemoryBufferRef mb, StringRef archiveName,
+                         uint64_t offsetInArchive)
+    : InputFile(BitcodeKind, mb) {
+  this->archiveName = std::string(archiveName);
+
+  std::string path = mb.getBufferIdentifier().str();
+  if (config->thinLTOIndexOnly)
+    path = replaceThinLTOSuffix(mb.getBufferIdentifier());
+
+  // ThinLTO assumes that all MemoryBufferRefs given to it have a unique
+  // name. If two archives define two members with the same name, this
+  // causes a collision which result in only one of the objects being taken
+  // into consideration at LTO time (which very likely causes undefined
+  // symbols later in the link stage). So we append file offset to make
+  // filename unique.
+  StringRef name = archiveName.empty()
+                       ? saver.save(path)
+                       : saver.save(archiveName + "(" + path + " at " +
+                                    utostr(offsetInArchive) + ")");
+  MemoryBufferRef mbref(mb.getBuffer(), name);
+
+  obj = CHECK(lto::InputFile::create(mbref), this);
+
+  Triple t(obj->getTargetTriple());
+  ekind = getBitcodeELFKind(t);
+  emachine = getBitcodeMachineKind(mb.getBufferIdentifier(), t);
+}
+
+static uint8_t mapVisibility(GlobalValue::VisibilityTypes gvVisibility) {
+  switch (gvVisibility) {
+  case GlobalValue::DefaultVisibility:
+    return STV_DEFAULT;
+  case GlobalValue::HiddenVisibility:
+    return STV_HIDDEN;
+  case GlobalValue::ProtectedVisibility:
+    return STV_PROTECTED;
+  }
+  llvm_unreachable("unknown visibility");
+}
+
+template <class ELFT>
+static Symbol *createBitcodeSymbol(const std::vector<bool> &keptComdats,
+                                   const lto::InputFile::Symbol &objSym,
+                                   BitcodeFile &f) {
+  StringRef name = saver.save(objSym.getName());
+  uint8_t binding = objSym.isWeak() ? STB_WEAK : STB_GLOBAL;
+  uint8_t type = objSym.isTLS() ? STT_TLS : STT_NOTYPE;
+  uint8_t visibility = mapVisibility(objSym.getVisibility());
+  bool canOmitFromDynSym = objSym.canBeOmittedFromSymbolTable();
+
+  int c = objSym.getComdatIndex();
+  if (objSym.isUndefined() || (c != -1 && !keptComdats[c])) {
+    Undefined newSym(&f, name, binding, visibility, type);
+    if (canOmitFromDynSym)
+      newSym.exportDynamic = false;
+    Symbol *ret = symtab->addSymbol(newSym);
+    ret->referenced = true;
+    return ret;
+  }
+
+  if (objSym.isCommon())
+    return symtab->addSymbol(
+        CommonSymbol{&f, name, binding, visibility, STT_OBJECT,
+                     objSym.getCommonAlignment(), objSym.getCommonSize()});
+
+  Defined newSym(&f, name, binding, visibility, type, 0, 0, nullptr);
+  if (canOmitFromDynSym)
+    newSym.exportDynamic = false;
+  return symtab->addSymbol(newSym);
+}
+
+template <class ELFT> void BitcodeFile::parse() {
+  std::vector<bool> keptComdats;
+  for (StringRef s : obj->getComdatTable())
+    keptComdats.push_back(
+        symtab->comdatGroups.try_emplace(CachedHashStringRef(s), this).second);
+
+  for (const lto::InputFile::Symbol &objSym : obj->symbols())
+    symbols.push_back(createBitcodeSymbol<ELFT>(keptComdats, objSym, *this));
+
+  for (auto l : obj->getDependentLibraries())
+    addDependentLibrary(l, this);
+}
+
+void BinaryFile::parse() {
+  ArrayRef<uint8_t> data = arrayRefFromStringRef(mb.getBuffer());
+  auto *section = make<InputSection>(this, SHF_ALLOC | SHF_WRITE, SHT_PROGBITS,
+                                     8, data, ".data");
+  sections.push_back(section);
+
+  // For each input file foo that is embedded to a result as a binary
+  // blob, we define _binary_foo_{start,end,size} symbols, so that
+  // user programs can access blobs by name. Non-alphanumeric
+  // characters in a filename are replaced with underscore.
+  std::string s = "_binary_" + mb.getBufferIdentifier().str();
+  for (size_t i = 0; i < s.size(); ++i)
+    if (!isAlnum(s[i]))
+      s[i] = '_';
+
+  symtab->addSymbol(Defined{nullptr, saver.save(s + "_start"), STB_GLOBAL,
+                            STV_DEFAULT, STT_OBJECT, 0, 0, section});
+  symtab->addSymbol(Defined{nullptr, saver.save(s + "_end"), STB_GLOBAL,
+                            STV_DEFAULT, STT_OBJECT, data.size(), 0, section});
+  symtab->addSymbol(Defined{nullptr, saver.save(s + "_size"), STB_GLOBAL,
+                            STV_DEFAULT, STT_OBJECT, data.size(), 0, nullptr});
+}
+
+InputFile *createObjectFile(MemoryBufferRef mb, StringRef archiveName,
+                            uint64_t offsetInArchive) {
+  if (isBitcode(mb))
+    return make<BitcodeFile>(mb, archiveName, offsetInArchive);
+
+  switch (getELFKind(mb, archiveName)) {
+  case ELF32LEKind:
+    return make<ObjFile<ELF32LE>>(mb, archiveName);
+  case ELF32BEKind:
+    return make<ObjFile<ELF32BE>>(mb, archiveName);
+  case ELF64LEKind:
+    return make<ObjFile<ELF64LE>>(mb, archiveName);
+  case ELF64BEKind:
+    return make<ObjFile<ELF64BE>>(mb, archiveName);
+  default:
+    llvm_unreachable("getELFKind");
+  }
+}
+
+void LazyObjFile::fetch() {
+  if (mb.getBuffer().empty())
+    return;
+
+  InputFile *file = createObjectFile(mb, archiveName, offsetInArchive);
+  file->groupId = groupId;
+
+  mb = {};
+
+  // Copy symbol vector so that the new InputFile doesn't have to
+  // insert the same defined symbols to the symbol table again.
+  file->symbols = std::move(symbols);
+
+  parseFile(file);
+}
+
+template <class ELFT> void LazyObjFile::parse() {
+  using Elf_Sym = typename ELFT::Sym;
+
+  // A lazy object file wraps either a bitcode file or an ELF file.
+  if (isBitcode(this->mb)) {
+    std::unique_ptr<lto::InputFile> obj =
+        CHECK(lto::InputFile::create(this->mb), this);
+    for (const lto::InputFile::Symbol &sym : obj->symbols()) {
+      if (sym.isUndefined())
+        continue;
+      symtab->addSymbol(LazyObject{*this, saver.save(sym.getName())});
+    }
+    return;
+  }
+
+  if (getELFKind(this->mb, archiveName) != config->ekind) {
+    error("incompatible file: " + this->mb.getBufferIdentifier());
+    return;
+  }
+
+  // Find a symbol table.
+  ELFFile<ELFT> obj = check(ELFFile<ELFT>::create(mb.getBuffer()));
+  ArrayRef<typename ELFT::Shdr> sections = CHECK(obj.sections(), this);
+
+  for (const typename ELFT::Shdr &sec : sections) {
+    if (sec.sh_type != SHT_SYMTAB)
+      continue;
+
+    // A symbol table is found.
+    ArrayRef<Elf_Sym> eSyms = CHECK(obj.symbols(&sec), this);
+    uint32_t firstGlobal = sec.sh_info;
+    StringRef strtab = CHECK(obj.getStringTableForSymtab(sec, sections), this);
+    this->symbols.resize(eSyms.size());
+
+    // Get existing symbols or insert placeholder symbols.
+    for (size_t i = firstGlobal, end = eSyms.size(); i != end; ++i)
+      if (eSyms[i].st_shndx != SHN_UNDEF)
+        this->symbols[i] = symtab->insert(CHECK(eSyms[i].getName(strtab), this));
+
+    // Replace existing symbols with LazyObject symbols.
+    //
+    // resolve() may trigger this->fetch() if an existing symbol is an
+    // undefined symbol. If that happens, this LazyObjFile has served
+    // its purpose, and we can exit from the loop early.
+    for (Symbol *sym : this->symbols) {
+      if (!sym)
+        continue;
+      sym->resolve(LazyObject{*this, sym->getName()});
+
+      // MemoryBuffer is emptied if this file is instantiated as ObjFile.
+      if (mb.getBuffer().empty())
+        return;
+    }
+    return;
+  }
+}
+
+std::string replaceThinLTOSuffix(StringRef path) {
+  StringRef suffix = config->thinLTOObjectSuffixReplace.first;
+  StringRef repl = config->thinLTOObjectSuffixReplace.second;
+
+  if (path.consume_back(suffix))
+    return (path + repl).str();
+  return std::string(path);
+}
+
+template void BitcodeFile::parse<ELF32LE>();
+template void BitcodeFile::parse<ELF32BE>();
+template void BitcodeFile::parse<ELF64LE>();
+template void BitcodeFile::parse<ELF64BE>();
+
+template void LazyObjFile::parse<ELF32LE>();
+template void LazyObjFile::parse<ELF32BE>();
+template void LazyObjFile::parse<ELF64LE>();
+template void LazyObjFile::parse<ELF64BE>();
+
+template class ObjFile<ELF32LE>;
+template class ObjFile<ELF32BE>;
+template class ObjFile<ELF64LE>;
+template class ObjFile<ELF64BE>;
+
+template void SharedFile::parse<ELF32LE>();
+template void SharedFile::parse<ELF32BE>();
+template void SharedFile::parse<ELF64LE>();
+template void SharedFile::parse<ELF64BE>();
+
+} // namespace elf
+} // namespace lld